1. Field of the Invention
The present invention relates to I/O bus technology, specifically, parameter exchange for a link layer.
2. Description of the Related Art
As is well known, input/output (I/O) buses connect different components together in a computer system. One example of an I/O bus is a link, which is a point-to-point interconnect connecting two components (these components can be on the same circuit board or across two different boards). A link could be bi-directional and consists of an out-going direction and an in-coming direction. Likewise, the width of the link is scalable from one bit (a.k.a. serial) to multiple bits in parallel. A single bit is transferred from the source component via a transmitter and received at the destination via a receiver. In the multi-bit parallel links, multiple bits are transferred simultaneously in parallel through multiple transmitter and receiver pairs. The signaling technology can be single-ended or differential. One example of a link is depicted in FIG. 1.
PCI-express and SCID links exchange physical layer operation parameters by embedding the component value in the special training sequences. For reference, PCI-express is discussed in “PCI-express Base Specification Rev 1.0, Jul. 22, 2002”. Each component then examines the incoming value and compares with its outgoing value. Based on a predetermined schedule, the two components would arrive at a final agreed value. For example, the PCI-Express links exchange its data rate, the number of training sequences required, link polarity and the reset condition in its initialization phase. However, a change in the protocol is required in order to support parameter negotiation in the PCI-express or the SCiD physical layer method. Furthermore, both methods only permit exchange of fixed number of parameters with no ability to expand.
Typically, external agents are involved for reading capabilities of different link interfaces and setting link operation registers.